To provide the mobile users with a higher data rate, the Long Term Evolution Advance (LTE-A) proposed a Carrier Aggregation (CA) technology aiming at providing a greater broadband for the user equipment with corresponding capacity so as to enhance the peak rate of the UE. In the LTE, the maximal downlink transmission bandwidth supported by the system is 20 MHz. The carrier aggregation is used to aggregate two or more Component Carriers (CC) for the purpose of supporting a downlink transmission bandwidth higher than 20 MHz but lower than 100 MHz. FIG. 1 is the schematic diagram of the carrier aggregation according to related art. The component carriers for carrier aggregation can be either continuous or discontinuous in frequency domain. The LTE-A using the carrier aggregation technology is a multi-carrier system.
In the mobile communication system, the UE can move between the cells. To ensure the service continuity and quality, after the user establishes a service, the UE is required to conduct measurement according to the configuration of the service base station and report the measurement report meeting the configuration requirement of the service base station so that the service base station can conduct reasonable switching determination according to the measurement report reported by the UE and other Radio Resource Management (RRM) algorithms, namely choose reasonable target cell to conduct switching so as to meet the mobility requirement.
In the connection state, the measurement behavior of the UE is controlled by the base station. The specific measurement process includes the following steps:
At Step 1, the network side (for example, a service base station) transmits the measurement control message to the UE, wherein the measurement control message includes a Measurement Object (MO) list, comprising the LTE frequency requiring measurement, each frequency is identified uniquely with a MOID (meansobjectId); a measurement Report Configuration (RC) list, comprising the attributes of each report configuration, for example, the measurement report is reported based on events or cycles, the corresponding configuration parameters, for example, the event type of the event-based reporting and the related parameters of the event type and the Time To Trigger (TTT) of the event-based reporting, wherein each report configuration is identified uniquely with a RCID (reportConfigId); a Measurement ID (MID) list, wherein the MID represents the identification of each specific measurement task, in the MID list, each MID is associated with a MOID and a RCID to represent one measurement task uniquely, namely represent the report configuration information of certain frequency uniquely. Besides, the measurement control information also includes the measurement threshold (s-Measure) which represents the signal quality threshold residing in the cell; the measurement Quantity Configuration, used to indicate the specific measurement quantity; and the Measurement Gap Configuration, used for the configuration of different frequency and different system.
At Step 2, the UE receives the measurement control message and gets the quantity of the measurement tasks through the quantity of the MIDs and the attributes of each measurement task through the MOID and the RCID corresponding to the MIDs, namely the MO and RC information of each measurement task.
At Step 3, the UE conducts measurement according to the configuration of the measurement control message and reports the measurement report meeting the RC configuration of each measurement task.
With respect to the measurement task whose report configuration (RC) is reported based on events, the UE measures the configured frequency (MO) and conducts an event evaluation to the measurement result of each cell measured on this frequency. If the measurement results of the cells are confirmed to meet the configured event entry condition of the RC within the configured TTT time thereof, and the cells have not been saved, the UE will locally save the cells meeting the entry condition and its measurement results in a cell list (cellsTriggeredList) identified with the MID of this measurement task, and transmit the measurement report generated by the UE to the network side after obtaining the best N cells regulated in the RC from the cell list in the order from strong to weak signal quality. Then, when the UE conducts an event evaluation and determines that the cells meeting the configured event exit condition of the RC within the configured TTT time thereof exist in the cell list, it will delete the cells meeting the exit condition and the measurement results thereof from the cell list. If there is no cell saved in the cell list after the deletion, the cell list identified by this MID will be deleted locally by the UE.
In an LTE system, to ensure its communication quality, the UE is required to measure the service cell all the time in the connection state. While for the adjacent cell, especially for the adjacent cell of different frequency and different system, the UE will consume extra electricity when conducting measurement. If the UE has only one radio frequency receiving equipment, it is allowed only to adjust the radio frequency receiving equipment from the service cell to the adjacent cell in the measurement gap configured by the base station so that its communication in the service cell is not affected. Moreover, the frequent measurement reporting of the UE will also occupy too many radio resources. Therefore, in order to meet the mobile demand of the UE in the connection state without consuming too much electricity or affecting its communication in the service cell, in an LTE system, the service base station will determine whether to configure different frequency/system measurement for the UE according to its signal quality in the service cell. Specifically, the configuration can be conducted in accordance with the following strategy: determine whether the UE conducts/stops the measurement task of different frequency/system according to the measurement results of the measurement events aiming at the service cell and configured for the UE by the base station—Event A1 (the signal quality of the service cell is larger than the threshold) and Event A2 (the signal quality of the service cell is smaller than the threshold). When the base station receives Event A2 reported by the UE, it will configure different frequency/system measurement tasks for the UE; while the base station receives Event A1 reported by the UE, it will delete the different frequency/system measurement tasks previously configured for the UE.
In an LTE system, to ensure its communication quality, when the UE is switched to the adjacent cell, the signal of the adjacent cell shall be sufficient to provide a secure communication quality for the UE. Therefore, the base station is required to configure measurement events aiming at the adjacent cell for the UE, such as Event A3 (the signal quality of the adjacent cell is an offset better than that of the service cell) and Event A5 (the signal quality of the service cell is smaller than threshold 1, and the signal quality of the adjacent cell is larger than threshold 2). These events are a kind of comparative event which needs to take the signal quality of both the service cell and the adjacent cell into consideration. When the base station receives the measurement reports of Event A3 or A5 reported by the UE, it can determine whether to switch the UE to the adjacent cell according to the switching determination as per the measurement report and other RRM algorithms.
In the carrier aggregation, the base station can configure the information of several carriers (called the configured carrier or work carrier) for the UE, and activate all or part of the carriers to let the UE conduct data transmission on the activated carriers. These carriers are known as activated carriers, while other configured carriers which have not been activated are known as deactivated carriers.
When providing the UE of the carrier aggregation with a larger bandwidth and a higher data rate, the electricity consumption of the UE is one of the problems requiring great consideration in related art of the carrier aggregation design. Therefore, to ensure the communication quality of the UE without consuming too much electricity, the base station in the carrier aggregation is also required to consider the signal quality of each activated carrier to determine whether to configure different frequency/system measurements for the UE. The switching of the UE to the adjacent cell will lead to the short-time interruption of the data transmission of the UE in the service cell and even certain loss of the data. Moreover, the switching process itself will cause great system overhead. Therefore, except some special strategies (for example, load balance) of the operators, unless the data transmission quality of the UE cannot be ensured in the service cell or the base station confirms that there is a adjacent cell better than the present service cell, the base station will not switch the UE to the adjacent cell. In the carrier aggregation, the base station is also required to consider the signal quality of each activated carrier comprehensively to determine whether to switch the UE to the adjacent cell so as to minimize unnecessary switching.
The inventor finds that, in related art, when the UE detects any measurement task configured by the base station meeting the trigger condition, for example, the service cell meets the entry or exit trigger conditions of the related events (Event A1 and A2) or the adjacent cell meets the entry trigger conditions of the comparative events (Event A3 and A5), it will generate a measurement report and report it to the base station, namely, the strategy of immediately reporting of all the measurement tasks as soon as they are triggered. However, this reporting method lacks flexibility when being used in the carrier aggregation.